Round cells and batteries made therefrom



Jan. 7, 1969 KNlGHT 3,420,714

ROUND CELLS AND BATTERIES MADE THEREFROM Filed June 21, 1965 In ventor GEOFFREY P- KNIGHT United States Patent 3,420,714 ROUND CELLS AND BATTERIES MADE THEREFROM Geoffrey Peter Knight, Loughton, England, assignor to The Ever Ready Company (Great Britain) Limited,

London, England, a corporation of Great Britain Filed June 21, 1965, Ser. No. 465,319 'Claims priority, application Great Britain, June 24, 1964,

26,212/64 US. Cl. 136-107 7 Claims Int. Cl. H01m 1/02; H01m 21/06; H01m 15/00 ABSTRACT OF THE DISCLOSURE This invention relates to galvanic dry cells.

A commonly used type of galvanic cell comprises a zinc can (soluble electrode), a coaxial carbon rod (insoluble electrode), and a bobbin of a depolarizer which fits over the carbon rod and is only prevented from contacting the inner wall of the can by a paper separator.

The top of the carbon rod projects somewhat above the top of the can and is provided with a flanged metal cap which is push-fitted thereonto. A bitumastic seal of considerable thickness closes the head space in the can to prevent loss of electrolyte and escape of moisture. Since the seal adheres to the can severe increases in pressures in the cell may fracture the bitumastic seal so that the depolarizer is no longer prevented from drying out.

A disability of such cells is the possibility of seepage of electrolyte through the top of the cell particularly during periods of rapid discharge of the cell.

In course of time too, the electrolyte makes the can wall sufficiently porous to cause seepage through the wall and eventually, by chemical action, binds the cell to the article, e.g. a flash light casing in which it has been used.

To reinforce the bitumastic seal a cardboard washer is incorporated thereabove in the head-space, and to form a seal at the top of the can the latter has been provided with a cardboard jacket, the top of which is folded into a lock joint made between the top of the can and a metal annulus which bears on the radial flange on the cap of the carbon rod and is electrically insulated therefrom by a cardboard washer.

Such cells are relatively expensive to produce and the formation of the lock joint at the top of the cells involves use of a zinc can of sufficient height to produce the metal to be used in the lock joint.

It has also been proposed to coat zinc cans to be used in cell manufacture to prevent the adverse effects of porosity already described by applying a coating by injection moulding methods. The can, however, must be fitted onto a fitting support in the mould to prevent the can being distorted by the usual high pressures used and the coated can must be separated from the support without distortion of any kind. Even so the jacket could not be effective to prevent seepage if the bitumen seal was broken.

Because of the lack of mechanical strength in the zinc can used conventional injection moulding methods are prima facie unsuitable because of the pressure used.

The main object of the present invention is to produce an improved leak proof cell.

According to the present invention a galvanic dry cell comprising a can (soluble electrode), a coaxial carbon rod (insoluble electrode), a depolarizer bobbin about the rod and a separator between the bobbin and the can wall, the rod carrying a metal cap, is characterized by a chamber above the depolarizer and another located by a wall formation near the top of the can.

The invention also comprises a leak proof cell constructed as just described encapsulated by injection moulding methods at relatively low temperatures and pressures using a synthetic plastics material which is sufliciently mobile at low temperature so that low moulding pressures and temperatures are used to effect encapsulation and when set has suflicient coherence at normal, even tropical, temperatures to retain the pristine seal.

By encapsulation, seepage at the top of the cell is eliminated and the adverse effects of porosity in the cell wall prevented. Moreover, the requisite moisture in the depolarizer is retained though a bitumastic seal is avoided.

Suitable synthetic plastic materials for use according to the invention in making a leak proof cell are low molecular weight polyethylene, they are mobile at quite low temperatures (130 C.l C.) and on setting have sufii cient coherence to retain the required hermetic seal over the cell to prevent loss of moisture from the depolarizer.

Furthermore, certain types of nylon as well as a copolymer of polyvinyl acetate and polyethylene (Elvax) or mixtures of polyethylene with parafiln wax, for example, 50% by weight of polyethylene and 50% by weight of paraffin wax, can be injection moulded onto dry cells and batteries comprising the dry cells using low temperatures, for example, to C., and pressures of the order of 100 lbs. to lbs. per sq. in. not exceeding, for example, -200 lbs. per sq. in. These low pressures compare with pressures of the order of 20,000 lbs. per sq. in. which are conventionally employed.

These materials have a low thermal capacity whilst the injection moulding machine, which may be water cooled for example, has a high thermal capacity so that coating materials mobile at temperatures higher than a battery or round cell could withstand if exposed to such temperatures in an oven for example, can be used because these coating materials rapidly give up their heat during the moulding process before they can injure the cell or battery. In operating in accordance with the present invention, synthetic plastics materials are chosen so that they are injection moulded onto the cell under conditions which in no way harm the cell.

In order that the invention may be more clearly understood a preferred embodiment thereof will now be described by Way of example with reference to the accompanying diagrammatic drawings in which:

FIGURE 1 is an elevation, partly in section, of a round cell constructed in accordance with the invention,

FIGURE 2 is an underside plan view of the round cell,

FIGURE 3 is a plan view of the top of the round cell, and

FIGURE 4 shows an assembled round cell in a mould (shown in section) ready for coating by injection moulding.

Referring first to FIGURES l, 2 and 3 of the drawings.

There is shown a round cell of the Leclanche type comprising a zinc can 1 as the soluble electrode and a coaxial carbon rod 2, capped by a brass cap 3, as the insoluble electrode. The zinc can 1 contains a conventional bobbin 4 of depolarizer and electrolyte, above which is a cardboard washer 5 located on the carbon rod 2 and of a diameter to engage the inner face of the can 1.

The zinc can 1 is formed near its upper end with an inwardly directed circumferential groove 6 in which groove rests a spacing washer 8 formed from an electrically insulating material, for example, polystyrene, the upper end of the can wall is turned inwardly onto the washer 8 to hold it firmly in position. The washer is designed to remain rigid and intact during the moulding of a plastic coating onto the round cell to hermetically seal the cell as hereinafter described.

The washers 5 and 8 define an expansion chamber 9, in the upper part of the can for reception of any gas and/ or electrolyte exuded by the depolarizer during rapid discharge of the cell and during production of a coating on the cell, as hereinafter described.

From the foregoing it will be appreciated that the cell constructed according to the invention and prepared for coating does not include the conventional bitumastic seal and accordingly the cell is lighter than a corresponding conventional dry cell.

The round cell so constructed is hermetically sealed by a coating 10 which coating envelops the can wall and extends under the bottom wall 11 of the can 1 to a limited extent, as shown in FIGURE 1, as well as over the spacing washer 8 and over the flange 12 of the cap 3, the overlap of the coating on the bottom 11 of the can 1 being such that a central part is uncovered to have an area for electrical connection to be made thereto, for example with cap 3 of another cell arranged in series relation.

As shown in FIGURE 2 the coating 10 preferably goes over and underneath the flange 12 on the brass cap 3 so that the flange becomes incorporated in the coating but does not pass between the spacing washer 8 and the carbon rod. Accordingly the coating 10 hermetically seals the cell and insulates the upper end 6 of the zinc can 1 from the carbon rod 2 and the brass cap 3.

The coating is formed from a synthetic plastics material, for example polyethylene, which is inert and impervious to electrolyte so that no seepage of electrolyte can occur between the cap flange 12 and the upper end 6 of the can 1. The moulded coating is in intimate contact with the area of the round cell which it covers due to the tension in the coating inherent in the method of forming the coating and the ensuing contraction of the coating in situ. The coating is not truly adhesive and experiments have shown that if the coating is slit parallelly to the carbon rod the coating opens away from the slit.

The method of forming the coating, i.e. by an injection moulding procedure, is such that intimate contact with the round cell wall that it closely follows even microeccentricities in the wall surface, thus the coating is to be differentiated from a round cell enclosed in a preformed sheath of synthetic plastics material where there is a definite gap between the zinc bucket 1 and the sheath.

A round cell fully assembled, as already described, is placed in a mould formed in two separate hollow parts 13 and 14 capable of being clamped together to form a mold.

The bottom 11 of the zinc container 1 is supported in the mould part 13 by a coaxial boss 15 which covers the central part of the bottom 11 to prevent the central part being coated. The other end of the round cell is engaged in the other mould part 14 by coaxial recess 16 which receives the cap 3 and prevents molten plastics material from forming a coating on the cap 3.

Molten synthetic plastics material is injected into the mould from a conventional injection moulding machine (not shown) through an inlet 17 and delivers the plastics material through radial inlets 18 of which two are shown, into a moulding cavity 19 enveloping the whole of the cell except the part abutting the boss 15.

When the round cell is located in the mould and the mould parts 13 and 14 are clamped together in fluidtight relationship, molten plastics material is injected into the mould using low temperatures and pressures to form a coating enveloping the cell and forming an hermetic seal thereover as already explained. The mould is then allowed to cool, the two parts 13 and 14 are separated and the round cell taken from the mould and stripped of sprue which is returned for re-use in the injection moulding machine.

Although the invention has been exemplified by reference to moulding a coating onto a single round cell, it will be understood that by suitably designing the moulds, two or more cells constructed according to the invention connected in parallel may be encapsulated to constitute an hermetically sealed battery, indeed any prescribed shape of the battery can :be moulded to include a plurality of interconnected cells, and it is to be understood that the present invention comprehends electrically connected batteries encapsulated together in the manner described.

If desired a false bottom plate may be added to each round cell and maintained in position by the coating, such plate may be embossed to ensure intimate contact between adjacent cells.

Furthermore, the leak proof battery is economically achieved; the complex interlocking equipment necessary to produce the conventional lock seam at the top of the can is not required, and the height of the can is at a minimum because of the absence of the conventional bitumastic seal, and accordingly a considerable saving in the amount of zinc required in forming the can is obtained.

I claim:

1. A galvanic dry cell comprising a can as the soluble electrode, a carbon rod as the insoluble electrode, a depolarizer bobbin about the rod and a separator between the bobbin and the can wall, the rod carrying a flanged metal cap, with a chamer above the depolarizer defined by a first insulating washer just above the depolarizer and a second insulating washer located by a wall formation near to the top of the can, and an injection moulded coating of synthetic plastics material encapsulating the engaging can and including a seal between the can rim and engaging said metal cap flange and also including a clamping flange overlying the marginal area of the base of the can, said seal and said clamping flange being integrally joined by a cylindrical portion of the coating which portion is in intimate contact with the whole cylindrical wall of the can including the region of said wall formation.

2. A process for producing a galvanic dry cell having as its main components a can as the soluble electrode, a carbon rod as the insoluble electrode, the carbon rod having a flanged metal cap, a depolarizer bobbin about the rod, and a separator between the bobbin and the can wall, characterized by the step of forming in one operation an integral coating which encapsulates the cell and which coating includes a seal between the can rim and said metal cap flange and also includes a clamping flange overlying the marginal area of the base of the can, said operation being effected by supporting the cell in a mould of capacity suflicient to allow the formation of the said coating around the cell, and injecting a synthetic plastics material at a temperature below C. and at a pressure below 200 p.s.i. into the mould to form the casing around the cell while cooling the mould, said plastics material being selected so as to be mobile at the said low temperatures.

3. A process according to claim 2, wherein the synthetic plastics material is a low molecular weight polyethylene.

4. A process according to claim 2, wherein the synthetic plastics material is a mixture of polyethylene with paraflin wax.

5. A process according to claim 4, wherein the plastics material is a mixture of 50% by weight of polyethylene and 50% by weight of parafiin wax.

6. A process according to claim 2, wherein the synthetic plastics material is nylon.

7. A process according to claim 2, wherein the synthetic plastics material is a copolymer of polyvinyl acetate and polyethylene.

References Cited UNITED STATES PATENTS 9/1947 Keller 13613'3 10/1948 Reinhardt et al 136133 10/1951 Lewis et a1 136-107 2/1960 Klopp 136-107 10/196'6 Reilly et a1 136107 3/1967 Fischer 264278 US. Cl. X.R. 

